In vapor compression systems comprising only one evaporator it is often attempted to control a mass flow of refrigerant supplied to the evaporator in such a manner that the potential refrigeration capacity of the evaporator is utilized to the maximum possible extent. On one hand, a large amount of gaseous refrigerant in the evaporator is undesirable, since it has an adverse effect on the refrigeration capacity of the evaporator because refrigeration takes place due to a phase transition of the refrigerant present in the evaporator. On the other hand, it is undesirable to allow liquid refrigerant to pass through the evaporator, because thereby the full refrigeration capacity of the refrigerant is not utilized, and because it might cause damage to the compressor. It is therefore desirable to control the mass flow of refrigerant to the evaporator in such a manner that a mixed phase of refrigerant, i.e. refrigerant comprising gaseous as well as liquid refrigerant, extents to a position which is as close as possible to an outlet of the evaporator, without allowing liquid refrigerant to pass through the evaporator. To this end the superheat (SH) at the outlet of the evaporator is often measured and used as a control parameter. A high superheat is a sign that too much gaseous refrigerant is present in the evaporator. A superheat which is zero is a sign that liquid refrigerant is allowed to pass through the evaporator. Accordingly, it is often attempted to control the mass flow of refrigerant supplied to the evaporator in such a manner that a minimal, but positive, superheat is obtained.
In vapor compression systems comprising two or more evaporators it may be a challenge to control the flow of refrigerant in the system in such a way that each of the evaporators is operated in an appropriate manner, and in such a way that the vapor compression system in general is operated efficiently, e.g. in the sense described above. More particularly, it is desirable to control such a vapor compression system in such a manner that the SH of each of the evaporators is controlled to be as near to zero as possible without allowing liquid refrigerant to pass through any of the evaporators. Furthermore, it is desirable to do this without significantly increasing the component count of the system.